And the בית יוסף wrote, "One must investigate the issue about our clothes that have two corners near the ground: why we don't put ציצית in them". And the רמ״א answered that because the commandment of ציצית is to put two before him and two behind him and our clothes have all four corners before him and cannot be worn another way, they are not obligated in ציצית; that's why they're accustomed to be lenient.